**1. Introduction**

Production-living-ecological space (PLES) is an important carrier for the survival and development of human society [1,2]. In recent years, with the development of territorial space planning in China, the PLES has attracted much academic attention, and research

**Citation:** Chen, H.; Yang, Q.; Su, K.; Zhang, H.; Lu, D.; Xiang, H.; Zhou, L. Identification and Optimization of Production-Living-Ecological Space in an Ecological Foundation Area in the Upper Reaches of the Yangtze River: A Case Study of Jiangjin District of Chongqing, China. *Land* **2021**, *10*, 863. https://doi.org/ 10.3390/land10080863

Academic Editor: Dong Jiang

Received: 18 July 2021 Accepted: 14 August 2021 Published: 17 August 2021

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on optimizing and coordinating the PLES has become a hot topic for scholars [3]. Along with the rapid development of industrialization and urbanization, the territorial spatial pattern of China has undergone profound changes since the reform and opening up [4–6]. At the same time, many space-related problems have arisen, such as extensive land use, environmental pollution and ecosystem degradation [7–9]. Therefore, the Nineteenth National Congress of the Communist Party of China (CPC) proposed scientifically delineating three control lines (an ecological protection red line, permanent basic farmland, and an urban development boundary) to coordinate the spatial pattern of production, living and ecology and promote the sustainable and balanced development of the economy and environment [10]. In this context, it is of great significance to identify and optimize the PLES to promote the sustainable development of territorial space, ecological civilization and beautiful China construction [11,12].

At present, scholars have carried out much research on the identification and optimization of the PLES and have achieved relatively fruitful results. The research content mainly focuses on the classification system of production-living-ecological land (PLEL) [13–16], the definition and connotation of the concept [17–20], the identification [2,21–23], reconstruction and optimization [24–26] and the pattern evolution of the PLES [27,28]. Qualitative and quantitative identification methods were used to identify and optimize the PLES from the perspectives of land use [21], rural settlements [18] and ecological landscapes [23]. The qualitative identification method mainly refers to the land use type merging method, which is based on the national land classification standard to classify and merge the status of land use, thereby identifying the PLES [29,30]. And the quantitative identification method refers to first constructing an index system and then using the entropy method [31], GIS spatial analysis method [22], coupling coordination degree model [1,22] and other methods or models to carry out functional evaluation and to identify and optimize the PLES. The former lacks consideration of the coordinated development of land use multifunctionality and functional coupling, while the latter has pertinence and comprehensive advantages but has not formed a unified standard system. The coordination of PLES is an effective way to optimize land use, the optimization method of land use in academia provides a good foundation for the study of PLES. At present, most scholars use genetic algorithm [32–34], multi-agent system (MAS) [35], artificial neural networks (ANN) [36] and other metrological methods to build land use optimization models and explore multiobjective optimization schemes for land use. In recent years, more and more scholars have analyzed the problems and the optimization mode of land use from the perspective of ecosystem services, so as to maximize the performance of ecosystem services and land use [37–40]. For example, Herzig [40] demonstrated a land use optimization model to improve ecosystem services by using the multi-objective spatial optimization method. Elliot [39] explored a land use scheme to maximize ecosystem services by optimizing urban land use allocation by using multi-objective integer linear programming (MOILP) model and land use/land cover (LULC) performance score.

Previous studies often used administrative units as the research scale, including macro scales such as the whole country, provinces and cities [25,31,41], meso scales such as cities and counties [42], and microscopic scales such as villages [28]. However, there are also large spatial differences in administrative units, especially in mountainous areas with complex topographical conditions. The spatial information reflected by the research based on the administrative unit scale is not detailed enough. Fortunately, the geographic grid can effectively compensate for this defect at the administrative unit scale [22]. In summary, current research on the identification and optimization of the PLES has achieved phased results, which provide a reference for this article. However, research based on the multifunctional coupling and coordination of land use is still insufficient, and current related research mostly uses the kilometer grid as the basic unit [43]. It is difficult to accurately identify the PLES. In addition, with the fine-grained geographic grid, the identification of the PLES needs to be strengthened.

It is necessary to ensure national ecological security and realize the coordinated development between economy and ecology by accurately identifying the PLES in the ecological barrier area of the upper reaches of the Yangtze River. Located at the upper reaches of the Yangtze River and the end of the Three Gorges Reservoir, Jiangjin District of Chongqing City undertakes the major task of constructing an ecological barrier. Moreover, Jiangjin District is located at the intersection of multiple strategic opportunities such as the construction of the Chengdu-Chongqing Double City Economic Circle, the coordinated development of One District and Two Groups of Chongqing and the construction of the co-urbanization of Chongqing. In the context of the construction of an ecological barrier in the upper reaches of the Yangtze River, and the superposition of multiple strategies, Jiangjin District is facing many development opportunities and challenges [44,45]. Whether socioeconomic, developmental or ecological and concerning environmental protection, it is necessary to use territorial space as a carrier. Therefore, the coordinated development of territorial space can provide a space guarantee for economic development and ecological protection. Therefore, how to optimize the territorial space and promote the sustainable development of the territorial space has become a key issue that urgently needs to be solved for Jiangjin District to consider development opportunities and strengthen ecological protection. In view of this, we selected Jiangjin District as the study area, established the evaluation system of the PLES and used the coupling coordination degree model to quantitatively calculate the coupling coordination degree of the PLEF of the study area. We identified the PLES by using a coupling coordination degree model. Finally, we propose the optimized partition scheme for territorial space based on the identification results. The purpose of this research is to provide a reference for the governance and optimization of territorial space in special areas of multiple strategic intersections.
